Copper-containing amine oxidases are widely distributed in nature and are involved in the metabolism of biogenic primary amines. Amine oxidases may have a variety of functions in the cardiovascular, gastrointestinal, and nervous systems of mammals. Amine oxidases are also responsible for the cross-linking of connective tissue structural proteins (elastin and collagen). It appears that numerous compounds with antifungal; antiprotozoal, or anticancer activities may target amine oxidases; for example pentamidine,a leading drug for the treatment of Pneumocystis carinii pneumonia (PCP) in AIDS patients belongs to class of compounds that inhibit amine oxidases. The principal goals are to determine the 3-D structures of multiple amine oxidases, including at least one human enzyme, and to elucidate the mechanisms of amine oxidation and cofactor (TPQ) biogenesis. In addition, the structure and biosynthesis of a related enzyme, galactose oxidase, will be examined. Site-directed mutagenesis, spectroscopy, kinetics measurements, and crystallography are employed. The crystal structures of two amine oxidases have been solved, revealing several novel features, including a second metal-binding site. Combining structural and mechanistic data WI permit a detailed understanding of the structure and function of these important enzymes to be developed.